U.S. Department of Justice
Office of Justice Programs
Bureau of Justice Statistics
------------------------------------------------------
This file is text only without graphics and many of
the tables. A Zip archive of the tables in this report
in spreadsheet format (.csv) and the full report
including tables and graphics in .pdf format are
available on BJS website at
https://www.bjs.gov/index.cfm?ty=pbdetail&iid=5986
This reports is one in series. More recent editions
may be available. To view a list of all reports in the
series go to https://www.bjs.gov/index.cfm?ty=pbse&sid=65
------------------------------------------------------
Crime Against Persons with Disabilities, 2009–2015 -
Statistical Tables
Erika Harrell, Ph.D., BJS Statistician
In 2015, the rate of violent victimization against persons with
disabilities (29.5 victimizations per 1,000 persons age 12 or
older) was 2.5 times higher than the rate for persons without
disabilities (11.8 per 1,000), which was adjusted to account for
the differences between the age distributions for persons with
and without disabilities (see Methodology) (figure 1).
***Footnote 1 Unless otherwise noted, the comparisons in this
report are significant at the 95% confidence level.*** In every
year from 2009 to 2015, the rate of violent victimization against
persons with disabilities was at least twice the age-adjusted
rate for persons without disabilities. The rate of violent
victimization increased from 2011 to 2012 for both persons with
and without disabilities. From 2012 to 2015, the rate remained
steady for persons with disabilities and decreased for persons
without disabilities.
This report details the rates of nonfatal violent victimization
against persons with and without disabilities, describes types of
disabilities, and compares victim characteristics. Nonfatal
violent crimes include rape or sexual assault, robbery,
aggravated assault, and simple assault. Findings are based on the
Bureau of Justice Statistics’ (BJS) National Crime Victimization
Survey (NCVS), a household survey that collects data on U.S.
residents age 12 or older (excluding those living in
institutions).
The NCVS adopted survey questions from the U.S. Census Bureau’s
American Community Survey (ACS) to identify crime victims with
disabilities. The NCVS defines disability as the product of
interactions among individuals’ bodies; their physical,
emotional, and mental health; and the physical and social
environment in which they live, work, or play. A disability
exists where this interaction results in limitations of
activities and restrictions to full participation at school,
work, home, or in the community. Disabilities are classified
according to six limitations: hearing (deafness or serious
difficulty hearing), vision (blindness or serious difficulty
seeing, even when wearing glasses), cognitive (serious difficulty
in concentrating, remembering, or making decisions because of a
physical, mental, or emotional condition), ambulatory (difficulty
walking or climbing stairs), self-care (a condition that causes
difficulty dressing or bathing), and independent living
(physical, mental, or emotional condition that impedes doing
errands alone, such as visiting a doctor or shopping).
Data from the ACS were used to estimate age-adjusted
victimization rates for persons without disabilities. Unless
noted, all rates for persons without disabilities are age
adjusted. The Methodology further details data sources,
computational procedures, and data limitations.
*****************
List of tables
*****************
Table 1. Rate of violent victimization and average annual number
of persons, by victim’s disability status and age, 2011–2015
Table 2. Rate of violent victimization against persons with and
without disabilities, by type of crime, 2011–2015
Table 3. Rate of violent victimization against persons with and
without disabilities, by victim characteristics, 2011–2015
Table 4. Rate of violent victimization against persons with
disabilities, by disability type and type of crime, 2011–2015
Table 5. Rate of violent victimization against persons with
disabilities, by disability type and sex, 2011–2015
Table 6. Percent of violent crime against persons with
disabilities, by type of crime and number of disability types,
2011–2015
Table 7. Rate of violent victimization, by number of disability
types and type of crime, 2011–2015
Table 8. Victim-offender relationship, by victim's disability
status, 2011–2015
Table 9. Time violent crime occurred, by victim's disability
status, 2011–2015
Table 10. Violent crime reported to police, by victim’s
disability status and disability type, 2011–2015
Table 11. Person who notified police of violent crime, by
victim's disability status, 2011–2015
Table 12. Reasons for not reporting violent crime to police, by
victim's disability status, 2011–2015
Table 13. Percent of violent victimizations in which assistance
from a nonpolice victim services agency was received, by victim's
disability status, 2011–2015
****************************
List of appendix tables
****************************
Appendix Tables 1. Unadjusted rates and standard errors of
violent victimization against persons without disabilities, 2009–
2015
Appendix Tables 2. Unadjusted rates and standard errors for
violent victimization against persons without disabilities, by
type of crime, 2011–2015
Appendix Tables 3 Unadjusted rates and standard errors for
violent victimization against persons without disabilities, by
victim characteristics, 2011–2015
Appendix Tables 4. U.S. population, according to the U.S. Census
Bureau's American Community Survey Public Use Microdata Sample
data, by disability status and demographic characteristics, 2011–
2015
Appendix Tables 5. Rates and standard errors for figure 1:
Violent victimization, by disability status, 2009–2015
Appendix Tables 6. Standard errors for table 1: Rate of violent
victimization and average annual number of persons, by victim's
disability status and age, 2011–2015
Appendix Tables 7. Standard errors for table 2: Rate of violent
victimization against persons with and without disabilities, by
type of crime, 2011–2015
Appendix Tables 8. Standard errors for table 3: Rate of violent
victimization against persons with and without disabilities, by
victim characteristics, 2011–2015
Appendix Tables 9. Standard errors for table 4: Rate of violent
victimization against persons with disabilities, by disability
type and type of crime, 2011–2015
Appendix Tables 10. Standard errors for table 5: Rate of violent
victimization against persons with disabilities, by disability
type and sex, 2011–2015
Appendix Tables 11. Standard errors for table 6: Percent of
violent crime against persons with disabilities, by type of crime
and number of disability types, 2011–2015
Appendix Tables 12. Standard errors for table 7: Rate of violent
victimization, by number of disability types and type of crime,
2011–2015
Appendix Tables 13. Standard errors for table 8: Victim-offender
relationship, by victim's disability status, 2011–2015
Appendix Tables 14. Standard errors for table 9: Time violent
crime occurred, by victim's disability status, 2011–2015
Appendix Tables 15. Standard errors for table 10: Violent crime
reported to police, by victim’s disability status and disability
type, 2011–2015
Appendix Tables 16. Standard errors for table 11: Person who
notified police of violent crime, by victim's disability status,
2011–2015
Appendix Tables 17. Standard errors for table 12: Reasons for not
reporting violent crime to police, by victim's disability status,
2011–2015
Appendix Tables 18. Standard errors for table 13: Percent of
violent victimizations in which assistance from a nonpolice
victim services agency was received, by victim's disability
status, 2011–2015
****************************************************
Violent crime by victim’s age and disability status
****************************************************
* During the 5-year aggregate period from 2011 to 2015, for each
age group measured except persons age 65 or older, the rate of
violent victimization against persons with disabilities was at
least 2.5 times the unadjusted rate for those without
disabilities (table 1).
* Among persons age 65 or older, there was no statistically
significant difference between the rates of violent victimization
by disability status.
* Among those with disabilities, persons ages 12 to 15 (144.1 per
1,000 age 12 or older) had the highest rate of violent
victimization among all age groups measured.
*********************************
Violent crime by type of crime
*********************************
* The rate of violent victimization against persons with
disabilities (32.3 per 1,000 age 12 or older) was 2.5 times the
rate for persons without disabilities (12.7 per 1,000)
during 2011-15 (table 2).
* The rate of serious violent crime (rape or sexual assault,
robbery, and aggravated assault) for persons with disabilities
(12.7 per 1,000) was more than three times
the rate for persons without disabilities (4.0 per 1,000).
* The rate of simple assault against persons with disabilities
(19.6 per 1,000) was more than twice the rate for persons without
disabilities (8.7 per 1,000).
* Serious violent crime accounted for a greater percentage of
violence against persons with disabilities (39%) than violence
against persons without disabilities (32%) (not shown).
* One in 5 violent crime victims with disabilities believed they
were targeted due to their disability (not shown).
*****************************************************************
********************************************
Disability population in the United States
********************************************
Between 2011 and 2015, 14% of the U.S. population age 12 or older
living outside of institutions had a disability, according to the
U.S. Census Bureau’s American Community Survey (ACS) (appendix
table 4). Among noninstitutionalized persons with disabilities,
48% were male and 52% were female. Whites accounted for about 69%
of the population with disabilities, followed by blacks (14%),
Hispanics (11%), persons of other races (4%), and persons of two
or more races (2%). Forty-two percent of the population with
disabilities were age 65 or older, compared to 12% of the
population without disabilities. The 2011 to 2015 ACS population
estimates of persons by disability status were generated from the
Public Use Microdata Sample.
******************************
Use of age-adjusted rates
******************************
The differences in age distributions between the persons with and
without disabilities must be taken into account when making
direct comparisons of the violent victimization rate between the
two populations. The age distribution of persons with
disabilities differs considerably from that of persons without
disabilities, and violent crime victimization rates vary
significantly with age.
According to the ACS, persons with disabilities are generally
older than persons without disabilities. The age adjustment
standardizes the rate of violence against persons without
disabilities to show what the rate would be if persons without
disabilities had the same age distribution as persons with
disabilities.
***********************************************
Crime Victims with Disabilities Awareness Act
***********************************************
The Crime Victims with Disabilities Awareness Act, 1998 (P.L.
105-301) mandates that the National Crime Victimization Survey
(NCVS) include statistics on crimes against persons with
disabilities and the characteristics of these victims. The act
was designed “to increase public awareness of the plight of
victims of crime with developmental disabilities, to collect data
to measure the magnitude of the problem, and to develop
strategies to address the safety and justice needs of victims of
crime with developmental disabilities.” Section 5 of the act
directed the Department of Justice to include statistics relating
to “the nature of crimes against persons with developmental
disabilities; and the specific characteristics of the victims of
those crimes” in the NCVS. This report is a part of BJS’s series
on crime against persons with disabilities. More information can
be found on the BJS website.
****************************************************************
*************************************************
Violent crime by sex, race, and Hispanic origin
*************************************************
Sex
* For both males and females during 2011-15, the rate of violent
victimization was higher for persons with disabilities than for
those without disabilities (table 3).
* The rate of violent victimization against males with
disabilities was 31.8 per 1,000, compared to 14.1 per 1,000 males
without disabilities.
* For females with disabilities, the rate of violent
victimization was 32.8 per 1,000, compared to 11.4 per 1,000
females without disabilities.
* Among persons with disabilities, no statistically significant
difference by sex was found in the rate of violent victimization.
However, among those without disabilities, males (14.1 per 1,000)
had a higher rate than females (11.4 per 1,000).
****************************
Race and Hispanic origin
****************************
* For each racial and ethnic group measured, persons with
disabilities had higher violent victimization rates than persons
without disabilities during 2011-15.
* Among the racial groups examined, persons of two or more races
had the highest rates of violent victimization among persons with
disabilities (128.5 per 1,000) and without disabilities (33.6 per
1,000).
* There was no statistically significant difference between the
victimization rates of whites (30.8 per 1,000), blacks (30.8 per
1,000), Hispanics (29.3 per 1,000), and persons of other races
(28.2 per 1,000) with disabilities.
* Among persons without disabilities, blacks (18.2 per 1,000) had
a higher rate of violent victimization than whites (12.0 per
1,000), Hispanics (13.0 per 1,000), and persons of other races
(6.4 per 1,000).
*********************
Types of disability
*********************
* During 2011-15, persons with cognitive disabilities had the
highest rates of total violent crime (57.9 per 1,000), serious
violent crime (22.3 per 1,000), and simple assault (35.6 per
1,000) among the disability types measured (table 4).
* Persons with hearing disabilities (15.7 per 1,000) had the
lowest rates of total violent victimization among the disability
types examined.
* Persons with vision (11.3 per 1,000), ambulatory (13.1 per
1,000), and independent living (12.1 per 1,000) disabilities had
similar rates of serious violence.
* Among both males (55.4 per 1,000) and females (60.3 per 1,000),
those with cognitive disabilities had the highest rate of total
violent victimization among the disability types measured (table
5).
* Males and females had similar rates of total violent
victimization in every disability type measured, except
independent living disabilities.
* Among those with independent living disabilities, males (26.5
per 1,000 persons) had a lower rate than females (33.8 per 1,000
persons) (90% confidence level).
**********************************************
Violent crime by number of disability types
**********************************************
* During 2011-15, while 49% of persons with disabilities had
multiple disability types (not shown), an estimated 54% of
violence against persons with disabilities occurred against those
with multiple disability types (table 6).
* Sixty-five percent of rapes or sexual assaults against persons
with disabilities were committed against those with multiple
disability types, the highest percentage among the crime types
examined. ***Footnote 2 For offense definitions see Criminal
Victimization, 2015 (NCJ 250180, BJS web, October 2016, p15), and
Terms and Definitions: Victims (BJS web).***
* During 2011-15, persons with a single disability type (29.6 per
1,000) were less likely than persons with multiple disability
types (35.2 per 1,000) to be violently victimized (90% confidence
level) (table 7).
* The rate of serious violent crime against persons with a single
disability type (11.4 per 1,000) was less than the rate for
persons with multiple disability types (14.1 per 1,000).
* The rate of rape or sexual assault against persons with a
single disability type (1.4 per 1,000) was lower than the rate
for those with multiple disability types (2.8 per 1,000).
* Rates of robbery, aggravated assault, and simple assault did
not differ significantly by the number of disability types.
*******************************
Victim-offender relationship
*******************************
* A higher percentage of violence against persons with
disabilities (40%) was committed by persons the victims knew well
or who were casual acquaintances than against persons without
disabilities (32%) (table 8).
* A lower percentage of total violence against persons with
disabilities (30%) was committed by strangers than against
persons without disabilities (39%) during 2011-15.
* There was no statistically significant difference in the
percentage of total violence committed by intimate partners
(including spouses, ex-spouses, boyfriends, and girlfriends)
of victims with (15%) and without (13%) disabilities.
* Other relatives (including parents, children, and other
relatives) accounted for a higher percentage of violence against
persons with disabilities (10%) than persons without disabilities
(6%).
***************
Time of crime
***************
* For violent crime victims with and without disabilities during
2011-15, a higher percentage of violence occurred during the
daytime than nighttime (table 9). This was also true for the rate
of violent victimization against persons with disabilities (not
shown).
* Persons with disabilities (57%) and without disabilities (54%)
experienced similar percentages of violence in the daytime.
* Persons with disabilities (38%) experienced a lower percentage
of violence that occurred at nighttime than persons without
disabilities (43%) (90% confidence level).
*******************
Police reporting
******************
* There was no statistically significant difference in the
percentages of violent crime reported to police for victims with
(49%) and without (46%) disabilities during 2011-15 (table 10).
* Violence against persons with a single disability type (45%)
was less likely to be reported to the police than violence
against persons with multiple disability types (52%) (90%
confidence level).
* Violence against persons with ambulatory disabilities (55%) was
more likely to be reported to police than violence against persons
with vision (42%) and cognitive (47%) disabilities.
* The majority of violence against persons with (64%) and without
(62%) disabilities reported to the police was reported by the
victim (table 11).
* A household member other than the victim reported 6% of
violence against persons with disabilities to police, which was
smaller than the percentage reported for persons without
disabilities (10%).
* Victims with and without disabilities offered similar reasons
for not reporting to police (table 12).
* Twenty percent of unreported violence against persons with
disabilities was not reported because it was not important enough
to the victim. Twenty-one percent was not reported because the
victim did not think the police would help.
* Forty percent of unreported violence against persons with
disabilities was dealt with in another way.
*******************
Victim services
*******************
* During 2011-15, a greater percentage of violence against
persons with disabilities (12%) involved receipt of assistance
from a nonpolice victim service agency than violence against
persons without disabilities (8%) (table 13).
****************
Methodology
****************
Survey coverage
****************
The National Crime Victimization Survey (NCVS) is an annual data
collection conducted by the U.S. Census Bureau for the Bureau of
Justice Statistics (BJS). The NCVS is a self-report survey in
which interviewed persons are asked about the number and
characteristics of victimizations they experienced during the
prior 6 months. The NCVS collects information on nonfatal
personal crimes (rape or sexual assault, robbery, aggravated
assault, simple assault, and personal larceny) and household
property crimes (burglary, motor vehicle theft, and other theft)
both reported and not reported to police. In addition to
providing annual level and change estimates on criminal
victimization, the NCVS is the primary source of information on
the nature of criminal victimization incidents.
Survey respondents provide information about themselves (e.g.,
age, sex, race and Hispanic origin, marital status, education
level, and income) and whether they experienced a victimization.
The NCVS collects information for each victimization incident
about the offender as perceived by the victim (e.g., sex, race,
Hispanic origin, age, and victim-offender relationship),
characteristics of the crime (including time and place of
occurrence, use of weapons, nature of injury, and economic
consequences), whether the crime was reported to police, reasons
the crime was or was not reported, and experiences with the
criminal justice system.
The NCVS is administered to persons age 12 or older from a
nationally representative sample of households in the United
States. The survey defines a household as a group of persons who
all reside at a sampled address. Persons are considered household
members when the sampled address is their usual place of
residence at the time of the interview and when they have no
usual place of residence elsewhere. Once selected, households
remain in the sample for 3 years, and eligible persons in these
households are interviewed every 6 months either in person or
over the phone for a total of seven interviews.
Generally, all first interviews are conducted in person, with
subsequent interviews conducted either in person or by phone. New
households rotate into the sample on an ongoing basis to replace
outgoing households that have been in the sample for a 3-year
period. The sample includes persons living in group quarters
(such as dormitories, rooming houses, and religious group
dwellings) and excludes persons living in military barracks and
institutional settings (such as correctional or hospital
facilities) and persons who are homeless.
In 2007, the NCVS adopted questions from the U.S. Census Bureau’s
American Community Survey (ACS) to measure the rate of
victimization against persons with disabilities. The NCVS does
not identify persons in the general population with disabilities.
*** Footnote 3 Beginning in July 2016, questions about disability
status of victims were removed from the crime incident form of
the NCVS. The questions were placed on the screener questionnaire
to ask about the disability status of the general
noninstitutionalized household population.*** The ACS
Subcommittee on Disability Questions developed the disability
questions based on those used in the 2000 Decennial Census and
earlier versions of the ACS. The questions identify persons who
may require assistance to maintain their independence, be at risk
for discrimination, or lack opportunities available to the
general population because of limitations related to a prolonged
(i.e., 6 months or longer) sensory, physical, mental, or
emotional condition. More information about the ACS and the
disability questions is available on the U.S. Census Bureau’s
website at
https://www.census.gov/people/disability/methodology/acs.html.
Changes to the disability questions in
the NCVS and ACS in 2008
***************************************
In 2008, the U.S. Census Bureau changed some of the disability
questions on the ACS. The question about sensory disability was
separated into two questions about blindness and deafness, and
the questions about physical disability asked only about serious
difficulty walking or climbing stairs. Also, questions on
employment disability and going outside of the home were
eliminated in 2008. Analysis of 2007 and 2008 ACS disability data
by the U.S. Census Bureau revealed significant conceptual and
measurement differences between the 2007 and 2008 disability
questions. The U.S. Census Bureau concluded that data users
should not compare the 2007 estimates of the population with
disabilities to those of later years. Because the 2007 and 2008
NCVS disability questions mirrored the ACS disability questions,
estimates of victimization of persons with disabilities from the
2007 and 2008 NCVS should not be compared. As a result, the 2007
disability data are not presented in this report. Further
explanation about incomparability of the 2007 and 2008 ACS
disability data is available at
https://www.census.gov/people/disability/files/2008ACS_disability
.pdf.
Disability questions included in the
NCVS between 2009 and 2015
***************************************
Questions 169a through 173
169a. Are you deaf or do you have serious difficulty hearing?
169b. Are you blind or do you have serious difficulty seeing,
even when wearing glasses?
170a. Because of a physical, mental, or emotional condition, do
you have serious difficulty—
* concentrating, remembering, or making decisions
* walking or climbing stairs
* dressing or bathing?
170b. Because of a physical, mental, or emotional condition, do
you have difficulty doing errands alone, such as visiting a
doctor’s office or shopping?
171. Is “Yes” marked in any of 169a-170b? (That is, has the
respondent indicated that he/she has a health condition or
disability?)
172. During the incident you just told me about, do you have
reason to suspect you were victimized because of your health
condition(s), impairment(s), or disability(ies)?
173. What health conditions, impairments, or disabilities do you
believe caused you to be targeted for this incident?
Age limitation on independent living
disabilities
***************************************
In the ACS, persons ages 12 to 14 are not asked about having an
independent living disability and are, therefore, excluded from
the populations with independent living disabilities. Even though
crime victims ages 12 to 14 receive this question in the NCVS
(question 170b), victims ages 12 to 14 who respond affirmatively
are excluded from rates of violent victimization against
persons with an independent living disability to match the age
limitations for having an independent living disability in the
ACS (age 15 or older). In this report, rates of violence against
persons with an independent living disability are per 1,000
persons age 15 or older, compared to rates per 1,000 persons age
12 or older for other disability types. Also, violent crime
victims ages 12 to 14 who report in the NCVS that they have an
independent living disability and no other disability type are
classified as not having a disability, to be compatible with age
limits on the disability definitions in the ACS.
Limitations of the estimates
***************************************
The NCVS was designed to measure the incidence of criminal
victimization against the U.S. civilian household population,
excluding persons who live in institutions and the homeless.
Institutions include adult correctional facilities, juvenile
facilities, nursing or skilled nursing facilities, inpatient
hospice facilities, residential schools for persons with
disabilities, and hospitals with patients who have no usual home
elsewhere. The measures of crime against persons with
disabilities (as measured by the NCVS) cover only persons with
disabilities who are living among the general population in
household settings. Subsequently, there is some coverage error in
using solely the noninstitutionalized population. For example,
according to the ACS, about 95% of the 1.3 million persons age
65 or older living in institutions had disabilities in 2015 (not
shown). Because persons in these facilities would not be covered
in the NCVS, estimates of violence against these persons were not
counted. The lack of information from the institutions will
result in an undercount of violence against persons with
disabilities.
Certain aspects of the NCVS design can also contribute to
underestimating the level or type of violence against persons
with disabilities. For example, the survey instruments, modes of
interview, and interviewing protocols used in the NCVS may not be
suited for interviewing persons who have difficulty
communicating, especially by telephone. Some persons have
disabilities that limit their verbal communication and use
technology to enhance their ability to communicate, but many
persons do not have access to such technology.
Proxy interviews may also lead to an underestimate of violence
against persons with disabilities. The survey requires direct
interviews with eligible respondents but allows the use of proxy
interviews with a caregiver or other eligible party in a limited
set of circumstances. A proxy interview is allowed when a
respondent is physically or mentally incapable of responding. The
survey restrictions on proxy interviews were instituted because
someone else may not know about the victimization experiences of
the respondent, or because the person providing the information
via proxy may be the perpetrator of the violence experienced by
the respondent. Because proxy respondents may be more likely to
omit crime incidents or may not know some details about reported
incidents, the number or types of crimes against persons with
disabilities may be underestimated.
In 2015, information from about 6% of violent crime incidents
against persons with disabilities was obtained from proxy
interviews. In addition, 76% of the reports of violent incidents
against persons with disabilities obtained through proxy
interviews were for simple assault, compared to about 58% of
reports of violent incidents against persons with disabilities
obtained through nonproxy interviews (not shown).
Public Use Microdata Sample data
***************************************
To generate populations by disability status between 2008 and
2015, Public Use Microdata Sample (PUMS) data from the U.S.
Census Bureau’s ACS were used to calculate populations by
disability status. The ACS PUMS dataset is a sample of population
and housing unit records from the ACS. Usually, the PUMS files
include about two-thirds of the cases contained in the larger,
complete confidential dataset. The ACS PUMS files include the
actual responses collected in ACS questionnaires, although some
responses have been edited to protect the confidentiality of
respondents. The ACS PUMS file included sample weights for each
person and housing unit, which were applied to the individual
records to expand the sample to estimate totals and percentages
of the full population. For more information on ACS PUMS data
from the U.S. Census Bureau, see https://www.census.gov/programs-
surveys/acs/technical-documentation/pums.html.
Direct standardization
***************************************
To generate age-adjusted rates of violent victimization of
persons without disabilities, direct standardization was used
with the population with disabilities as the standard population.
*** Footnote 4 For more information on direct standardization,
see Curtin, L. R. & Klein, R. J. (1995). Direct standardization
(age-adjusted death rates). Healthy People 2000: Statistical
Notes, 6 Revised. Available at
https://www.cdc.gov/nchs/data/statnt/statnt06rv.pdf.*** This
procedure eliminates the problem of different age distributions
between and within groups. In general, persons with disabilities
are an older population than persons without disabilities.
Because of this and due to the fact that crime rates vary by age,
direct standardization produces age-adjusted rates for persons
without disabilities that would occur if the population without
disabilities had the same age distribution as the population with
disabilities.
The age-adjusted violent victimization rate, using direct
standardization (Rd), is calculated as--
Rd = Σ (wa * ra)
where
Rd = age-adjusted rate of violent victimization of the population
without disabilities calculated using direct standardization
wa = weight calculated from the population with disabilities for
age-group a
ra = unadjusted rate of violent victimization of persons without
disabilities in age-group a.
The weight (wa) for age-group a is calculated as—
wa = na / N
where
wa = weight calculated from the population with disabilities for
age-group a
na = number of persons in age-group a in the population with
disabilities
N = total number of persons in the population with disabilities.
In figure 1, for each year, unadjusted rates were calculated for
persons with disabilities. For persons without disabilities,
rates were age-adjusted to the population with disabilities for
that year. For example, the 2014-15 rate of violent victimization
against persons with disabilities was unadjusted. The 2014-15
rate of violent victimization against persons without
disabilities was age-adjusted using the 2014-15 population with
disabilities as the standard population.
Change in direct standardization
calculations
***************************************
In previous BJS reports about crimes against persons with
disabilities, several different methods were used to calculate
age-adjusted rates. More specifically, changes in the standard
population were made. In the past, the population without
disabilities and the 2000 U.S. standard population generated by
the U.S. Census Bureau have both been used as the standard
population in calculating age-adjusted rates for persons with and
without disabilities. Each time a change was made to the standard
population, rates for all years were recalculated using the new
standard population. This resulted in previous years having
different rates from earlier reports.
Nonresponse and weighting adjustments
***************************************
In 2015, about 95,760 households and 163,880 persons age 12 or
older were interviewed for the NCVS. Each household was
interviewed twice during the year. The response rate was 82% for
households and 86% for eligible persons. Victimizations that
occurred outside of the United States were excluded from this
report. In 2015, less than 1% of the unweighted victimizations
occurred outside of the United States and were excluded from the
analyses.
Estimates in this report use data from the 2008 to 2015 NCVS data
files weighted to produce annual estimates for persons age 12 or
older living in U.S. households. Because the NCVS relies on a
sample rather than a census of the entire U.S. population,
weights are designed to inflate sample point estimates to known
population totals and to compensate for survey nonresponse and
other aspects of the sample design.
The NCVS data files include both household and person weights.
The household weight is commonly used to calculate estimates of
property crimes, such as motor vehicle theft or burglary, which
are identified with the household. Person weights provide an
estimate of the population represented by each person in the
sample. Person weights are most frequently used to compute
estimates of crime victimizations of persons in the total
population. After proper adjustment, both household and person
weights are also used to form the denominator in calculations of
crime rates.
The victimization weights used in this analysis account for the
number of persons present during an incident and for repeat
victims when a series of incidents occurs. The weighting counts a
series of incidents as the actual number of incidents reported by
the victim, up to a maximum of 10 incidents. Series
victimizations are victimizations that are similar in type but
occur with such frequency that a victim is unable to recall each
individual event or to describe each event in detail. Survey
procedures allow NCVS interviewers to identify and classify these
similar victimizations as series victimizations and collect
detailed information on only the most recent incident in the
series. In 2015, series incidents accounted for about 1% of all
victimizations and 4% of all violent victimizations. The approach
to weighting series incidents as the number of incidents up to a
maximum of 10 produces more reliable estimates of crime levels,
while the cap at 10 minimizes the effect of extreme outliers on
the rates. Additional information on the series enumeration is
detailed in the report Methods for Counting High Frequency Repeat
Victimizations in the National Crime Victimization Survey (NCJ
237308, BJS web, April 2012).
Standard error computations for
percentages and unadjusted rates
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When national estimates are derived from a sample, as is the case
with the NCVS, caution must be taken when comparing one estimate
to another or when comparing estimates over time. Although one
estimate may be larger than another, estimates based on a sample
have some degree of sampling error. The sampling error of an
estimate depends on several factors, including the amount of
variation in the responses, the size of the sample, and the size
of the subgroup for which the estimate is computed. When the
sampling error around the estimates is taken into consideration,
estimates that appear different may not be statistically
different.
One measure of the sampling error associated with an estimate is
the standard error. The standard error can vary from one estimate
to another. In general, for a given metric, an estimate with a
smaller standard error provides a more reliable approximation of
the true value than an estimate with a larger standard error.
Estimates with relatively large standard errors are associated
with less precision and reliability and should be interpreted
with caution.
To generate standard errors around numbers and estimates from the
NCVS, the U.S. Census Bureau produces generalized variance
function (GVF) parameters for BJS. GVFs take into account aspects
of the NCVS complex sample design and represent the curve fitted
to a selection of individual standard errors based on the
Jackknife Repeated Replication technique. GVF parameters were
used to generate standard errors for each point estimate (such as
counts, percentages, and unadjusted rates) in this report. For
estimates, standard errors were based on the ratio of the sums of
victimizations and respondents across years.
BJS conducted tests to determine whether differences in estimated
percentages and unadjusted rates in this report were
statistically significant once sampling error was taken into
account. Using statistical programs developed specifically for
the NCVS, all comparisons in the text were tested for
significance. The primary test procedure was the Student’s t-
statistic, which tests the difference between two sample
estimates. Unless otherwise noted, the findings described in this
report as higher, lower, or different passed a test at the 0.05
level of statistical significance (95% confidence level).
Findings that passed a test at the 0.10 level of significance are
noted as such in the text (90% confidence level). Caution is
required when comparing estimates not explicitly discussed in
this report.
Data users can use the estimates and the standard errors of the
estimates provided in this report to generate a confidence
interval around the estimate as a measure of the margin of error.
The following example illustrates how standard errors can be used
to generate confidence intervals:
According to the NCVS, between 2011 and 2015, 53.6% of violent
crime against persons with disabilities involved victims with
multiple disability types (see table 6). Using GVFs, BJS
determined that the estimate has a standard error of 2.14% (see
appendix table 11). A confidence interval around the estimate
was generated by multiplying the standard error by ±1.96 (the
t-score of a normal, two-tailed distribution that excludes 2.5%
at either end of the distribution). Therefore, the confidence
interval around the 53.6% estimate is 53.6% ± 2.14% × 1.96 (or
49.44% to 57.83%). In other words, if we used the same sampling
method to select different samples and computed an interval
estimate for each sample we would expect the true population
parameter (percent of violent crime against persons with
disabilities in which the victim had multiple disability types)
to fall within the interval estimates 95% of the time.
In this report, a coefficient of variation (CV), representing the
ratio of the standard error to the estimate, was also calculated
for all estimates. CVs provide a measure of reliability and a
means for comparing the precision of estimates across measures
with differing levels or metrics. In cases where the CV was
greater than 50%, or the unweighted sample had 10 or fewer cases,
the estimate was noted with a “!” symbol. (Interpret data with
caution. Estimate based on 10 or fewer sample cases, or
coefficient of variation is greater than 50%.)
Standard error computations and statistical
significance for age-adjusted rates
********************************************
Due to the complexity in generating age-adjusted rates of violent
crime, other methods were used to compute standard errors and
determine statistical significance. *** Footnote 5 For more
information on computing standard errors for age-adjusted rates,
see Anderson, R. N., & Rosenberg, H. M. (1998). Age
standardization of death rates: Implementation of the year 2000
standard. National Vital Statistics Reports, 47 (3). Available at
https://www.cdc.gov/nchs/data/nvsr/nvsr47/nvs47_03.pdf. *** The
standard error for the age-adjusted rate of violent victimization
against persons without disabilities was calculated as--
Sd = √Σ (wa2 * va)
where
Sd = standard error for an age-adjusted rate of violent
victimization against persons without disabilities that was
computed using direct standardization
wa = weight calculated from the population with disabilities for
age group a
va = variance calculated for an unadjusted rate of violent
victimization of persons without disabilities for age group a
using information from the GVF parameters that the Census Bureau
produced for the NCVS.
To calculate statistical significance among rates with at least
one age-adjusted rate, the standard error for the age adjusted
rate was calculated using the formula above. A Student’s t-
statistic also was calculated, which tests the difference between
two sample estimates. Unless otherwise noted, the findings
described in this report as higher, lower, or different passed a
test at the 0.05 level of statistical significance (95%
confidence level). Findings that passed a test at the 0.10 level
of significance are noted as such in the text (90% confidence
level).
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The Bureau of Justice Statistics of the U.S. Department of
Justice is the principal federal agency responsible for measuring
crime, criminal victimization, criminal offenders, victims of
crime, correlates of crime, and the operation of criminal and
civil justice systems at the federal, state, tribal, and local
levels. BJS collects, analyzes, and disseminates reliable and
valid statistics on crime and justice systems in the United
States, supports improvements to state and local criminal justice
information systems, and participates with national and
international organizations to develop and recommend national
standards for justice statistics. Jeri M. Mulrow is acting
director.
These statistical tables were prepared by Erika Harrell. Shannan
Catalano provided verification.
Caitlin Scoville and Jill Thomas edited the report. Steve
Grudziecki produced the report.
July 2017, NCJ 250632
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Office of Justice Programs
Building Solutions * Supporting Communities * Advancing Justice
www.ojp.usdoj.gov
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